Gold was one of the earliest metals available to man due to the relative ease with which large particles of gold can be recovered.
Alluvial gold, or particles found in sand and silt, can be recovered by a density gradient separation technique. Gold is a heavy element which settles faster than other lighter particles. This facilitates its recovery when it reaches the bottom of the recovery "apparatus" as the first species. Ore may be recovered in a similar fashion but must be crushed first. Both are recovered fairly efficiently with current methods.
There are problems, however, in extraction of gold from lower grade ores, waste-rock dump materials, slime-dam residues and scrap materials, as traditional recovery methods are designed to extract only large, coarse gold deposits. Cyanidation, until recently, has been the only alternative to remove small particles of gold from slime on an industrial scale. As the demand for gold increases, processing of lower grade ores, slime residues, waste solutions containing gold and the like to extract gold therefrom needs to be accomplished with greater efficiency.